1. Field of the Invention
The present invention relates to an X-ray computed tomography (CT) method and apparatus for obtaining panoramic X-ray images of an object to be examined seen from an optional direction by radiating a conical X-ray beam on a part of the object to be examined.
2. Prior Art
A method of obtaining a panoramic X-ray image known as X-ray computer tomography (CT) has been widely used in medical practice as for diagnosis. This method involves radiating X-rays on the object from all around, followed by analyzing a three-dimensional absorption coefficient distribution information, namely a three-dimensional distribution information of an X-ray absorption coefficient, on the X-rayed object from the projection data by the Radon theory as widely known, thereby obtaining a sectional image of object.
The prior art X-ray CT is a technique in which a fan-shaped X-ray beam relatively wide in the direction of rotation and thin is radiated on the object from around at a depth and this is repeated at different depths.
Accordingly, in the event that only a part inside the object is to be put to tomography examination, the fan-shaped wide X-ray beam is radiated over the whole object to obtain a three-dimensional distribution information of an X-ray absorption coefficient from which a three-dimensional distribution information of an X-ray absorption coefficient on that part or region is taken out for analysis. That is, the object is exposed to a substantial dose of the X-ray beam. In addition, it takes long to radiograph and analyze the test data. Accordingly in the light of high dose of radiation, the CT examination is limited to some once a year.
The applicant of the present invention proposes an X-ray computer tomography (CT) method and apparatus for solving the problem of exposed dose of the X-ray beam, namely by radiating conical X-ray beams of a small section area onto a local region, the object to be examined, only once, the three-dimensional distribution information of an X-ray absorption coefficient of the local region is calculated out.
FIG. 24a is a plane view conceptually showing the area of the three-dimensional distribution information of an X-ray absorption coefficient obtained by the X-ray CT apparatus, FIG. 24b is a partial plane view for conceptually showing the method for producing panoramic X-ray images from the three-dimensional distribution information of an X-ray absorption coefficient and FIG. 24c is a partial view of the panoramic X-ray image produced by this method.
In FIG. 24a, S is a dental arch and SA is a curved sectional area along the dental arch S and is covered by oblique lines. According to the X-ray CT apparatus, a distribution information of an X-ray absorption coefficient is obtained for the curved sectional area SA, which is an object to be examined. In this area SA, if a region is designated, the three-dimensional distributed information of an X-ray absorption coefficient at the region can be obtained. SB is a panoramic image layer of the curved sectional area SA. Lc is a normal line to the panoramic image layer SB. In FIG. 24b, H1 and H2 conceptually show foreign objects existing inside of a part of the dental arch S.
The X-ray CT apparatus enables the production of normal panoramic X-ray images as such shown in FIG. 24c by processing the three-dimensional distribution information of an X-ray absorption coefficient on the normal line Lc to the panoramic image layer SB shown in FIG. 24b. It also enables the production of sectional images of selected teeth, wherein the X-ray exposed dose is decreased to about 1 to 5% of that in case of using conventional systems.
But the panoramic X-ray images produced by the above mentioned method has one problem: as the production method of panoramic X-ray images is limited to the method shown in FIG. 24b, if there are any foreign materials H1 and H2 in the direction of a normal line LC, they are overlapped in the obtained panoramic X-ray image shown in FIG. 24c and cannot be distinguished. In addition, how a tooth is overlapped with another is sometimes invisible on a panoramic view produced from one direction.
The applicant of the present invention has proposed a panoramic X-ray picturing apparatus applicable to various dental arches in a Japanese patent application laid on unexamined under No. S60-103942. With this apparatus, the loci of the rotation of panoramic X-ray radiation can be adjusted depending on male, female or children examinees. The direction of normal lines to the dental arches is changeable depending on the size of the dental arch, and the problem derived from the fixed normal line mentioned above has been solved with that apparatus.
This apparatus, however, requires the loci of the rotation of panoramic X-ray radiation to be changed in order to obtain different panoramic X-ray images, so that the setting condition should be set before picturing. Another problem is that as this apparatus was not made for a computer tomography but for a conventional picturing of sectional images, it also requires the rotating center of the rotary arm to be moved along the specified loci during picturing, which needs a complex driving mechanism.
The applicant of this invention has also introduced in a Japanese patent application laid on unexamined under No. H4-144549 a digital panoramic X-ray picturing apparatus with which panoramic X-ray images of sectional image layers obliquely crossing the curved sectional image layers are produced.
This apparatus enabled the production of panoramic X-ray images seen from the oblique direction of the dental arch. It uses a frame image comprising the projection images and obtains partial images by shifting at a predetermined distance in accordance with the direction of the image shifting in a specific time period. Then the partial images are added to obtain a panoramic X-ray image seen from obliquely.
With this apparatus, however, the data from the obtained projection images is recalculated only after a digital processing and does not utilize the CT method computing a three-dimensional distribution information of an X-ray absorption coefficient by means of backprojection processing, so that the overlapped foreign materials H1 and H2 can not be distinguished.
The present invention has been proposed to solve the above-mentioned problems. According to which, a projection image taken by one X-ray picturing can be effectively utilized with all sorts of merits of X-ray computed tomography method and apparatus using a conical X-ray beam, and a panoramic X-ray image of one panoramic sectional image layer seen from an optional direction can be further gained.
The present invention has been developed to solve those problems as a result of intensive researches by the inventors and following (1)-(11) propose its method and (12)-(29) propose its apparatus.
In the X-ray CT of the present invention, a dental arch being an object to be examined is considered as a curved sectional area, an X-ray projection image is obtained for the curved sectional area by local radiation, the obtained X-ray projection image is processed by a backprojection method, and a three-dimensional distribution information of an X-ray absorption coefficient of the curved sectional area is calculated. Then the three-dimensional distribution information of an X-ray absorption coefficient is reconstructed by several methods, namely the three-dimensional distribution information of an X-ray absorption coefficient on a projection line intersecting a normal line of an area at an optional angle is calculated for the area on a panoramic image layer of the curved sectional area, the calculated result is expanded on a two-dimensional plane, and a panoramic X-ray image wherein the curved sectional area is seen from an optional projection line can be produced.
(1) An X-ray computed tomography method of the present invention is comprised of: sequentially obtaining on a two-dimensional X-ray image sensor an X-ray projection image information of a curved sectional area by photographing with a rotary arm turning while locally radiating conical X-ray beams constantly passing through only a specific region from an X-ray generator, conforming a rotating center of the rotary arm and a center of the specific region in the curved sectional area along a dental arc, which is an object to be examined, or inside of a bow-shape of the curved sectional area, the rotary arm including the X-ray generator and the two-dimensional X-ray image sensor facing to each other; arithmetically processing thus obtained X-ray projection image information by a backprojection method and computing a three-dimensional distribution information of an X-ray absorption coefficient of the curved sectional area; and calculating the three-dimensional distribution information of an X-ray absorption coefficient on a projection line intersecting a normal line of a panoramic image layer at a specified angle for any regions of the panoramic image layer of the curved sectional area and obtaining a panoramic X-ray image of the curved sectional area seen from the projection line by expanding the calculated result on a two-dimensional plane.
According to the X-ray CT method the rotary arm of following complicate loci doesn""t require to form an envelope curve La (as in FIG. 6) as in the prior art for producing panoramic X-ray images. In the present invention, radiographing is performed with the center of rotation fixed. at a specific region. Therefore, the construction of the rotary arm can be simplified.
In this method, a conical X-ray beam is always radiated on a specific region in the curved sectional area along a dental arc, which is an object to produce a panoramic X-ray image, or inside of a bow-shape of the curved sectional area. When a panoramic X-ray image of an entire jaw is radiographed, the specific region is required to be outside of the curved sectional region and inside of the bow-shape of the curved sectional area. When a panoramic X-ray image of one side such as a right side or a left side is radiographed, the specific region may be inside of the curved sectional area. In other words, according to this method, the curved sectional region to be radiographed to produce an image and the specific region where X-ray conical beams are always radiates locally are basically different.
While the projection data is small that can be obtained with the conical X-ray beam locally radiated on the curved sectional region to produce a panoramic X-ray image, panoramic X-ray images clear enough for use in practice can be obtained. That is because the specific region selected is an area in the curved sectional region or in the bow-shape of the curved sectional region where there are less obstacles and, in addition, only a required X-ray projection image is appropriately extracted from the X-ray projection image produced by the conical X-ray beams.
As an example of the specific region, the region which includes excursion of an ortho-conical X-ray beam necessary for producing an ortho-radial panoramic X-ray image of the curved sectional area, is suitable. However, it may be a region in the curved sectional area and in the bow-shape of the curved sectional area. The specific region may be determined considering the projecting condition such as an ortho-radial panoramic radiography by an orth-conical X-ray beam and a normal panoramic radiography and the exposure dose. It is understood that the ortho-conical X-ray beam is a shape of a conical X-ray beam that is locally radiated to produce panoramic X-ray images roughly perpendicular to the curved sectional area, an ortho-radial panoramic X-ray image and it means a conical X-ray beam roughly perpendicular to the panoramic image layer in the curved sectional area extracted from the locally radiating conical X-ray beam. The reason why that ortho-conical X-ray beam alone is extracted is this. The partial X-ray projection images by the ortho-conical X-ray beam contain projection data most suitable for formation of panoramic X-ray images of the curved sectional region, that is, projection data in which teeth are less overlapped.
After selecting such a specific region, only partial X-ray projection images produced by the ortho-conical X-ray beam roughly perpendicular to the curved sectional area is taken out from the X-ray projection images of the curved sectional area sequentially produced on the two-dimensiona X-ray image sensor. The taken out partial X-ray projection images are arithmetically processed to obtain the three-dimensional distribution information of an X-ray absorption coefficient of the dental arc. Thereby, clear ortho-radial panoramic X-ray images can be obtained.
Furthermore, in this method, because a panoramic X-ray image which is an overlapping image seen from a projection line intersecting at a specified angle to a panoramic image layer for producing the panoramic X-ray image is obtained, foreign objects hidden if seen from one direction can be easily found, and because diverse sectional images changing a direction of the projection line for a same sectional image layer is obtained, how a tooth is overlapped with another can be more accurately diagnosed.
In case of producing panoramic X-ray images, panoramic sectional images seen from different directions of a projection line for the same sectional image layer can be provided as mentioned above so that the method of the present invention is highly useful for diagnosis
(2) An X-ray computed tomography method is comprised of: sequentially obtaining on a two-dimensional X-ray image sensor an X-ray projection image information of a curved sectional area by photographing with a rotary arm turning while locally radiating conical X-ray beams constantly passing through only a specific region from an X-ray generator, conforming a rotating center of the rotary arm and a center of the specific region in the curved sectional area along a dental arc, which is an object to be examined, or inside of a bow-shape of the curved sectional area, the rotary arm including the X-ray generator and the two-dimensional X-ray image sensor facing to each other; arithmetically processing thus obtained X-ray projection image information by a backprojection method and computing a three dimensional distribution information of an X-ray absorption coefficient of the curved sectional area; and calculating the three-dimensional distribution information of an X-ray absorption coefficient on a projection line for any regions of the panoramic image layer of the curved sectional area, presetting a normal line of the panoramic image layer as the projection line, and obtaining a panoramic X-ray image of the curved sectional area seen from the projection line by expanding the calculated result on a two-dimensional plane.
This X-ray CT method defines the specified angle of the projection line and the normal line of the panoramic image layer in the X-ray CT method mentioned in (1) is set at 0 (zero) degree. Namely, the projection line conforms with the normal line.
In the prior panoramic X-ray imaging apparatus without using CT, an X-ray transmitted image including not only a three-dimensional distribution information of an X-ray absorption coefficient of a desired region for producing X-ray transmitted images but also information of an unnecessary region for producing images, therefore, the obtained images may be out of focus. Furthermore, X-ray incidence for a dental arch from a complete normal direction can""t be achieved. Therefore, the obtained images aren""t a complete ortho-radial panoramic X-ray image. However in this CT method, the three-dimensional distribution information of an X-ray absorption coefficient for the once obtained curved sectional area by local radiation is reconstructed so that only acceptable data among the obtained data, namely the data on a projection line while presetting a direction of a normal line for the panoramic image layer as a direction of the projection line, are used for producing a panoramic X-ray image, thereby an accurate ortho-radial panoramic X-ray image being obtained.
(3) According to this X-ray computed tomography method, in the X-ray computed tomography method in (1) or (2), a calculated result of a weighted average of the three-dimensional distribution information of an X-ray absorption coefficient on the projection line is expanded on a two-dimensional plane so as to obtain a panoramic X-ray image from the three-dimensional distribution information of an X-ray absorption coefficient of the curved sectional area.
According to this X-ray CT method, an operational method which isn""t specified in (1) and (2) is defined to be a weighted average. According to the weighted average, experimentally obtained weighting can be done for each data in case of calculating from the three-dimensional distribution information so that more accurate panoramic X-ray image can be obtained. If any weighing isn""t set for the weighted average, calculation is an arithmetic average.
(4) According to this X-ray computed tomography method, in the X-ray CT methods in (1) to (3), a direction of the projection line further becomes a direction of a normal line for a rising direction of each tooth constituting the dental arch corresponding to the curved sectional area.
The specified angle in (1) to (3) isn""t always two-dimensional but may include a three-dimensional one. In this method, the specified angle is defied as an angle in which the direction of the projection line is the direction of the normal line for the rising direction of tooth.
In the prior panoramic X-ray image, because front teeth are inclined for a sectional image layer, images in which adjacent teeth are overlapped are obtained or images of accurate size can""t be obtained. However, according to this method, images in which teeth are rarely overlapped can be obtained and accurate diagnosis of caries of adjacent teeth can be done, because images seen from the normal line of the rising direction of the teeth. Furthermore, caries diagnosis can be made at full scale.
(5) According to this X-ray computed tomography method, in the X-ray CT method in (1), the specified angle is constructed to be adjustable at an optional angle in up and down direction and/or right and left direction for the panoramic image layer. This method clears that the specified angle isn""t limited to be two-dimensional and may be a three-dimensional angle including an up and down direction and/or a right and left direction for the panoramic image layer, like the method in (4). The method can correspond to the case where the rising direction and the overlapping direction of teeth are three-dimensionally inclined such as in up and down direction and/or in right and left direction.
(6) According to the X-ray computed tomography method, the specified angle of the X-ray CT methods in (1) to (5) is constructed so as to be equal for any regions of the panoramic image layer. In the present invention, the specified angle of the projection line and the normal line of the panoramic image layer may be basically different depending on each region. In this method, the specified angle is set equal for the panoramic image layer.
In such a manner, panoramic X-ray images seen from a direction of the projection line inclining at an equal angle for any regions of the panoramic image layer so that the images can be sensuously understood. (7) According to this X-ray computed tomography method, either the specified angle described in the methods (1), (5) or (6) is infinitely and variably adjustable or it is selectable from plural specified angles.
In this method, a setting method of the specified angle for determining a direction of the projection line is defined. (8) According to the X-ray computed tomography method, in the X-ray CT methods in (1) to (7), the object to be examined is moved for the rotating center of the rotary arm or the rotating center of the rotary arm is moved for the object to be examined for positioning so as to conform the rotating center of the rotary arm and the center of the specific region. According to this method, a method for conforming the rotating center of the rotary arm and the center of the specified region can be selected from two ways according to the target to be moved so that there are plural choices for conforming those centers.
(9) According to the X-ray computed tomography method, in the X-ray CT methods in (1) to (8), only ortho-conical X-ray beams which is approximately perpendicular to the panoramic image layer are extracted from the conical X-ray beams and are radiated, a partial X-ray projection image information obtained on the two-dimensional X-ray image sensor by the ortho-conical X-ray beams is arithmetically processed by a backprojection method and the three-dimensional distribution information of an X-ray absorption coefficient of the curved sectional area is obtained, and a panoramic X-ray image is obtained by expanding the three-dimensional distribution information on a two-dimensional plane.
According to this method, radiating beam is an ortho-conical X-ray beam from the first instead of extracting a partial X-ray projection image information presumably obtained by ortho-conical X-ray beams from the X-ray projection image information after radiating conical X-ray beams. Therefore, the ortho-conical X-ray beams are included in the conical X-ray beams so that exposed dose to the object to be examined can be more reduced.
(10) According to the X-ray computed tomography method, in the methods described in (1) to (9), X-rays are radiated on an object to be examined while the rotary arm is turned with an axial direction of the rotating axis of the rotary arm inclining at a specified angle for a perpendicular direction of the object or the rotary arm is turned with the object inclining at a specified angle for the axial direction of the rotating arm of the rotary arm.
According to this method, conical X-ray beams are radiated on the object while the rotary arm is turned with the axial direction of the rotating axis of the rotary arm inclining at a specified angle for the perpendicular direction of the object or the rotary arm is turned with the object inclining at a specified angle for the axial direction of the rotating arm of the rotary arm. Therefore, conical X-ray beams can be radiated in a direction so as not to transmit a cervix which becomes an affecting shadow and the affect of the affecting shadow can be reduced. In the latter method, the apparatus can be simplified because the direction of the object is inclined.
(11) According to the X-ray computed tomography method, in the methods of (1) to (9) X-rays are radiated on the object to be examined while the rotary arm is turned while making the rotating axis a given precession movement.
According to this method, X-rays are radiated on the object while the rotary arm is turned while making the rotary axis of the rotary arm a given precession movement, namely grinding movement wherein the rotary axis is turned around the precession axis with the rotary axis inclining at a specified angle to the precession axis at a center of the specified region, so that conical X-ray beams can avoid the affecting shadow which can""t be avoided if they are radiated horizontally.
(12) An X-ray computed tomography apparatus is comprised of: a rotary arm with an X-ray generator and a two-dimensional image sensor faced to each other; position adjusting means for conforming a rotating center of the rotary arm and a center of a specific region in a curved sectional area along a dental arc, which is an object to be examined, or inside of a bow-shape of the curved sectional area; turning means for turning the rotary arm while locally radiating conical X-ray beams constantly passing through only the specific region from the X-ray generator; image storage means for sequentially storing an X-ray projection image information of the curved sectional area obtained on the two-dimensional X-ray image sensor by the X-ray conical beams; arithmetic processing means for calculating thus obtained X-ray projection image information by a backprojection method and computing a three-dimensional distribution information of an X-ray absorption coefficient of the curved sectional area; and angle setting means for setting a specified angle of a normal line of a panoramic image layer in the curved sectional area and a projection line intersecting the normal line; wherein the arithmetic processing means calculates the three-dimensional distribution information of the X-ray absorption coefficient on the projection line intersecting at the specified angle set by the angle setting means for any regions on the panoramic image layer, the calculated result is expanded on a two-dimensional plane, and a panoramic X-ray image of the curved sectional area seen from a direction of the projection line is obtained. This apparatus is to achieve the CT method of (1) and has the same effect as that of (1).
(13) An X-ray computed tomography apparatus is comprised of: a rotary arm with an X-ray generator and a two-dimensional image sensor faced to each other; position adjusting means for conforming a rotating center of the rotary arm and a center of a specific region in a curved sectional area along a dental arc, which is an object to be examined, or inside of a bow-shape of the curved sectional area, turning means for turning the rotary arm while locally radiating conical X-ray beams constantly passing through only the specific region from the X-ray generator; image storage means for sequentially storing an X-ray projection image information of the curved sectional area obtained on the two-dimensional X-ray image sensor by the conical X-ray beams; arithmetic processing means for calculating thus obtained X-ray projection image information by a backprojection method and computing a three-dimensional distribution information of an X-ray absorption coefficient of the curved sectional area; and angle setting means for setting a specified angle of a normal line of a panoramic image layer in the curved sectional area and a projection line intersecting the normal line; wherein the angle setting means sets the specified angle in such a manner that a direction of the projection line conforms to a direction of the normal line of the panoramic image layer for any regions on the panoramic image layer of the curved sectional area, the arithmetic processing means calculates the three-dimensional distribution information of the X-ray absorption coefficient on the projection line for the regions, the calculated result is expanded on a two-dimensional plane, and a panoramic X-ray image of the curved sectional area seen from a direction of the projection line is obtained.
This apparatus is to achieve the CT method of (2) and has the same effect as that of (2).
(14) According to the X-ray computed tomography apparatus, in the X-ray CT apparatus of (12) or (13), the arithmetic processing means expands a calculated result of a weighted average of the three-dimensional distribution information of the X-ray absorption coefficient on the projection line on the two-dimensional plane so as to obtain a panoramic X-ray image from the three-dimensional distribution information of the X-ray absorption coefficient of the curved sectional area.
This apparatus is to achieve the CT method of (3) and has the same effect as that of (3).
(15) According to the X-ray computed tomography apparatus, in the X-ray CT apparatus of (12) to (14), the angle setting means is further constructed in such a manner that a direction of the projection line also becomes a direction of a normal line for a rising direction of each tooth constituting the dental arch corresponding to the curved sectional area.
This apparatus is to achieve the CT method of (4) and has the same effect as that of (4).
(16) According to the X-ray computed tomography apparatus, in the X-ray CT apparatus of (12), the angle setting means is constructed in such a manner that the specified angle is adjustable at an optional angle in up and down direction and/or in right and left direction for the panoramic image layer. This apparatus is to achieve the CT method of (5) and has the same effect as that of (5).
(17) According to the X-ray computed tomography apparatus, in the X-ray CT apparatus of (12) or (16), the angle setting means is constructed in such a manner that the specified angle is equal for any regions of the curved sectional area. This apparatus is to achieve the CT method of (6) and has the same effect as that of (6).
(18) According to the X-ray computed tomography apparatus, in the X-ray CT apparatus of (12), (16) or (17), the angle setting means is comprised of variable means for infinitely and variably adjusting the specified angle and/or selection means for selecting the specified angle from predetermined plural angles. This apparatus is to achieve the CT method of (7) and has the same effect as that of (7).
(19) According to the X-ray computed tomography apparatus, in the X-ray CT apparatuses of (12) to (18), the position adjusting means is constructed in such a manner that the object to be examined is moved for the rotating center of the rotary arm or the rotating center of the rotary arm is moved for the object to be examined for positioning so as to conform the rotating center of the rotary arm and the center of the specific region.
This apparatus is to achieve the CT method of (8) and has the same effect as that of (8).
(20) According to the X-ray computed tomography apparatus, the X-ray CT apparatuses of (12) to (19) is further comprised of X-ray beam width restriction means for extracting and radiating only ortho-conical X-ray beams which are approximately perpendicular to the panoramic image layer from the conical X-ray beams, and wherein the arithmetic processing means arithmetically processes a partial X-ray projection image information obtained on the two-dimensional X-ray image sensor by the ortho-conical X-ray beams by a backprojection method and the three-dimensional distribution information of the X-ray absorption coefficient of the curved sectional area is obtained, and a panoramic X-ray image is obtained by expanding thus obtained three-dimensional distribution information on the two-dimensional plane.
(21) According to the X-ray computed tomography apparatus, in the X-ray CT apparatuses of (12) to (20), X-rays are radiated on the object to be examined while the rotary arm is turned with the axial direction of the rotating axis of the rotary arm inclining at a specified angle for a perpendicular direction of the object by providing rotating axis direction setting means capable of inclining the axial direction of the rotating axis of the rotary arm or X-rays are radiated on the object to be examined while the rotary arm is turned with the object inclining at a specified angle for the axial direction of the rotating center of the rotary arm by providing object supporting direction setting means capable of inclining the object""s supporting direction.
This apparatus is to achieve the CT method of (10) and has the same effect as that of (10).
(22) According to the X-ray computed tomography apparatus, in the X-ray CT apparatuses of (12) to (20), the turning means is constructed in such a manner that the rotary arm is turned while making the rotating axis of the rotary arm a given precession movement.
This apparatus is to achieve the CT method of (11) and has the same effect as that of (11).
(23) According to the X-ray computed tomography apparatus, in the X-ray CT apparatuses of (12) to (22), the curved sectional area is any one of a local region where a few teeth are rising, a temporomandibular joint region or an otorhinolaryngologic region.
According to this apparatus, the curved sectional area is one of a local region where a few teeth are rising, a temporomandibular joint region or an otorhinolaryngologic region. In this case, panoramic X-ray images seen from optional projection lines can be obtained for these regions in a same manner.
(24) According to the X-ray computed tomography apparatus, the X-ray CT apparatuses of (12) to (23) are further comprised of display means capable of sequentially displaying the panoramic X-ray image obtained while setting the specified angle by means of the angle setting means.
This apparatus has display means capable of sequentially displaying the panoramic X-ray image obtained while changing the specified angle by means of the angle setting means. Therefore, the images in which a specified angle is seen from varied directions can be obtained according to diagnosis purposes so that such an apparatus has a high diagnosis value.
(25) According to the X-ray computed tomography apparatus, the display means of the X-ray CT apparatus in (24) can sequentially show the panoramic X-ray image obtained while continuously changing the specified angle by means of the variable means of the angle setting means described in (18).
According to this apparatus, the display means of (24) is defined to display panoramic X-ray images while continuously changing the direction of the projection line so that it has a high diagnosis value.
(26) According to the X-ray computed tomography apparatus, in the X-ray CT apparatus of (24), the display means can combine a panoramic X-ray image of an upper jaw and a panoramic X-ray image of a lower jaw, both obtained by the apparatus of (15), into one panoramic X-ray image for displaying, the panoramic X-ray image of the upper jaw being obtained by setting a normal line direction for a rising direction of a tooth of a curved sectional area along the upper jaw as a projection line and the panoramic X-ray image of the lower jaw being obtained by setting a normal line direction for a rising direction of a tooth of a curved sectional area along the lower jaw.
According to this apparatus, the CT method of (15) is separately used for the curved sectional area of the upper jaw and that of the lower jaw and the display means of (24) is defined to display one combined panoramic X-ray image of thus obtained panoramic X-ray image of the upper jaw and thus obtained panoramic X-ray image of the lower jaw. Therefore, images corresponding to each rising direction of teeth can be obtained so that such images have high a diagnosis value.
(27) According to the X-ray computed tomography apparatus, in the apparatuses of (24) to (26), the display means can select plural panoramic X-ray images obtained under different conditions and display in array on the same screen. According to this apparatus, as plural panoramic X-ray images can be selected and displayed in array on the same screen, displaying images can be selected according to diagnosis purposes, thereby achieving convenience.
(28) According to the X-ray computed tomography apparatus, in the apparatus of (27), the display means can display the panoramic X-ray image obtained in (12) and the panoramic X-ray image obtained in (13) in array on the same screen, the panoramic X-ray image obtained in (12) being seen from the projection line intersecting the normal line of the panoramic image layer at a specified angle and the panoramic X-ray image obtained in (13) being seen from the projection line by setting the normal line of the panoramic image layer as the projection line. According to this apparatus, the display means of (27) is defined to display in array the panoramic X-ray images seen from an optional direction of the projection line and the panoramic X-ray images seen from the normal line, like the prior art. Such an apparatus is useful for comparing and judging the images.
(29) According to the X-ray computed tomography apparatus, at least one of functions same as operated in the apparatuses of (12) to (28) can be selectively operated. Therefore, several types of panoramic X-ray images can be obtained and shown by one apparatus so that it is useful for diagnosis.